Environment
How a cocktail of invasive species and global change is altering the Great Lakes-St. Lawrence River ecosystem
Hundreds of waterfowl washed ashore. Decaying feathered lumps dotted the beaches and rocky shores of the Great Lakes. Geese, gulls and loons had drowned in their native waters, their paralyzed necks unable to lift their heads above the waves.
The first documented die-offs from avian botulism in Ontario’s Great Lakes were in Lake Michigan in 1963-64, just a few years after the St. Lawrence Seaway transformed the Great Lakes-St. Lawrence River into a 3,700-kilometre inland commercial shipping route for international vessels, the longest such system in the world and a major artery of North American trade.
But since 1999, the carcasses of drowned birds have piled up in the tens of thousands. On Lake Erie, the devastating die-offs have become a near yearly event.
Avian botulism — the strain of the potent toxin that affects birds — is common in low-oxygen environments, like wetlands and lakes, and has been known since the 1900s to cause mass die-offs in wild birds. But in the Great Lakes, the increasing frequency of these die-offs had scientists stumped. Why did the deaths accelerate? A study published in 2006 in the Journal of Wildlife Diseases, revealed the answer: a complicated series of interactions between invasive species, climate change and other environmental stressors created the ideal conditions for the deadly pathogen to gain a foothold and keep on climbing.
A trio of invasive species native to Eurasia played a starring role in the prevalence of the deadly neurotoxin in the food chain. Quagga and zebra mussels, introduced into the Great Lakes-St. Lawrence River basin in the 1980s from the ballast water of ships, filtered the water clear, allowing more sunlight to penetrate the surface. This led to a bloom of giant algal mats that, when they decomposed, began to suck oxygen from the water. Low oxygen coupled with warming waters due to climate change set the perfect conditions for botulism spores to germinate and then filter back through the mussels. Enter the next invasive species: the round goby, first spotted in the Great Lakes in 1990 and now one of the system’s foremost bottom-dwelling fish. Adult gobies fed on the toxic mussels, and the waterfowl dined on the gobies. The food chain was poisoned.
This story of disruption in the Great Lakes-St. Lawrence River basin is reflected all too well around the globe. Invasive species are now the second leading driver of extinction worldwide after habitat destruction. Across ocean and sea, from cliff to coast, these biological invasions are reshaping the planet’s biogeography as we know it.
The Great Lakes-St. Lawrence River basin now teems with nearly 200 invasive species; a steady transformation is occurring beneath the water’s surface. Is it too late to reverse course? That’s the billion-dollar question.
“The river is a lifeblood,” says Anthony Ricciardi, professor of environmental science at McGill University. “What happens to its ecology matters to everyone whether they realize it or not. It’s in our DNA. It’s in our poetry. It’s part of our culture.”
Like many Montrealers, Ricciardi grew up by the St. Lawrence. As a child in the early ’80s, he would fish on the river and was fascinated by the myriad creatures in its waters. But the St. Lawrence of today is very different from the river he knew. By the 1990s, the large river mussels abundant in Ricciardi’s youth had been decimated in many areas by the pervasive zebra mussel that now blankets kilometres of shoreline and covers the shells of other native molluscs.
“Under the water, it’s an ecological battlefield, where natives and nonnative species are fighting for space and resources,” Ricciardi says.
Although change is a constant in any ecosystem, for the past five decades the rate of the river’s change has been dangerously quick, too swift for scientists to grasp its full scope. The speed and scale of this species invasion is unprecedented, says Ricciardi. Species have always spread to new regions of the globe, but humans have accelerated that expansion. Both wittingly and unwittingly, we have allowed invasive species to gain footholds in every corner of the planet, from the deep sea to frozen mountain peaks.
“It has become a form of anthropogenic global change,” Ricciardi explains. “Its impact is felt in all ecosystems, in all regions of the planet, but it’s especially visible in large aquatic ecosystems like the Great Lakes-St. Lawrence River basin.”
At last count, the Great Lakes-St. Lawrence River basin was home to more than 180 non-native aquatic plants, animals and microorganisms. Those dominant invaders wreaking havoc with the waterfowl — zebra mussels, quagga mussels and round goby — all hail from the Black and Caspian seas and were introduced via the ballast tanks of transoceanic ships navigating the seaway. About 65 per cent of all basin invasions can be traced to ship ballast tanks, according to data analyzed by Ricciardi.
But commercial shipping is not the only vector. The story of invasives is a human story — a story of hubris and folly, ignorance and carelessness. The litany of introduced species in the region is a long one, stretching back decades, or more.
There’s invasive phragmites, an aquatic plant perhaps better known as the European common reed. Established in Canada in the early 20th century, phragmites quickly crowd out native vegetation, releasing toxins that kill other plants. Along the shores of Long Point, on the north side of Lake Erie, the plant spans just under 2,500 football fields of dense reeds of up to five metres tall, making it more difficult for at-risk native species like turtles and salamanders to move around.
A century ago, it was the sea lamprey in the spotlight for causing wide-scale destruction, invading the Great Lakes via shipping canals and causing the collapse of cisco and lake trout fisheries.
And a fish introduced to the southern United States in the 1960s and 1970s to control algal blooms in wastewater ponds and aquaculture pens is now on our radar as a massive threat to the Great Lakes. Four species of Asian carp escaped the facilities during flooding and established themselves in the Mississippi River Basin. Four decades later, two species — silver and bighead carp — have made their way north through a series of rivers that connect the Gulf of Mexico and Mississippi River to the Illinois Waterway, within striking distance of Lake Michigan. These carp are eating machines, consuming up to 40 per cent of their body weight every day and leaving little behind for pike, pickerel, walleye and bass.
In 1986, a Canadian businessperson illegally transported tench from Germany to his fish farm in southern Quebec. A few years later, some of the invasive sport fish escaped into the Richelieu River, a tributary of the St. Lawrence. Those tench have thrived in Lac-Saint-Pierre, a fluvial lake in the St. Lawrence just east of Montreal and one of the most important wetland areas in North America. They are now poised to invade the Great Lakes en masse — some have already been caught as far west as Lake Ontario’s Bay of Quinte.
In the early 2000s, fish started showing up dead due to the invasive pathogen known as viral hemorrhagic septicemia, which is believed to have hitchhiked to the St. Lawrence via ballast water. It is thought to have killed nearly half of the adult muskellunge in the upper St. Lawrence River, and caused large-scale die-offs of northern pike, yellow perch and walleye.
The list goes on and on and on, each biological invasion further altering a system already under siege.
“Invasive species are often incredibly aggressive,” says Sarah Rang, executive director of the Invasive Species Centre, a not-for-profit based in Sault Ste. Marie, Ont., that’s working to prevent and reduce the spread of invasive species. “They come to an area, they reproduce really quickly, they grow really quickly, and they have no natural predators. So, they just boom.”
It becomes a race against time as we try to cope with — or mitigate the effects of — a range of aquatic invaders. Between them, they damage water quality, render spaces less suitable for recreation, ruin infrastructure, and carry parasites and diseases harmful to human health. Each year, Canada spends an astonishing $7 billion on its aquatic invasive species response.
Climate change adds another dangerous element to the mix, with shrinking winter ice, warming surface water temperatures, and rising or dwindling water levels. The disruptive power of climate change is measured in the soil and essence of the Great Lakes-St. Lawrence River basin, and these alterations may draw invaders from near and afar.
“What would normally prevent a species from arriving could be its temperature tolerance,” says Becky Cudmore. The regional manager of the invasive species program at Fisheries and Oceans Canada, Cudmore is overseeing a project to track the effects of climate change on aquatic species. “If that barrier of temperature moves north because of climate change, then you’ve just created an opportunity for a species that would otherwise not be able to cross that temperature barrier to arrive in a new location.” In other words, warming bodies of water present a great opportunity for certain species, like Asian carp, to spread further north.
Beyond warming waters, more frequent extreme weather events also give invasive species a helping hand. “Hurricanes and floods can be a route of transportation for invasive species, especially for some plants,” says Rang. “They have little roots that can break off if you have a big flood. Those roots can travel easily from one place to another place, and then they can reestablish themselves in that new place.”
Indeed, a study published in Global Change Biology in 2020 provides a stark vision for the future, concluding that expanding trade and transport networks, when combined with the effects of climate change and tourism, will result in the number of established invaders around the globe increasing by 36 per cent by 2050.
But while the clock cannot be turned back on the Great Lakes- St. Lawrence River basin, people like Henry Lickers are working on adapting to the changing ecosystem. Lickers grew up in Six Nations of the Grand River, between Lake Ontario and Lake Erie. His people, the Seneca of the Haudenosaunee Confederacy, have lived on the St. Lawrence for 9,000 years. “You go out on the river, and it’s like looking at the veins in the back of your hand,” says Lickers, a Canadian commissioner at the International Joint Commission, an organization created by Canada and the United States to cooperatively manage and protect their shared lakes and rivers.
The International Joint Commission unites people on both sides of the Great Lakes-St. Lawrence River in managing invasive species through prevention, eradication, containment and control measures. But to Lickers, that’s only part of the equation. Combining western science with Indigenous knowledge needs to be part of the solution, he says. Indigenous knowledge systems take a broader, holistic view of the natural world, creating a better understanding of the bigger picture of an interconnected ecosystem.
Part of this knowledge is the understanding around adapting to the presence of new species. “It’s hard to put the genie back in the bottle,” he says. “When it invades us, how do we adapt? How do we use it?”
He notes that on a small scale, people in the Haudenosaunee community are creating an example; they harvest invasive plants like purple loosestrife to tan animal hides and make medicinal tea to treat stomach ailments. Broadening palates to consume carp or zebra mussels may be another way of bringing the ecosystem back into equilibrium. However, targeting individual invaders alone is not enough. “If I narrow it right down to the individual species, I’m never going to find the answer. The impact on one little species blooms out so big that you just don’t see all of the implications.”
Ricciardi agrees. “We have to stop thinking of invasions as one event at a time. They’re not isolated monster stories. They’re all symptomatic of a form of global change.”
Back in his laboratory, Ricciardi and his students are conducting experiments to determine how certain native and invasive species in the Great Lakes-St. Lawrence River basin will respond to warmer surface water temperatures in the coming decades. The idea is to determine whether “today’s winners are tomorrow’s losers, or whether today’s benign species are tomorrow’s problems,” he says.
Although predictions are difficult to make, the bigger picture is already clear — reducing the rate of invasion decreases the chances of future devastation. “If you can reduce the influx of invaders, then you reduce the probability and magnitude of the next ecological bomb going off,” he says.
The story of the Great Lakes-St. Lawrence River basin is still being penned, with invasive species at the centre of a massive transformation constantly altering the region’s ecosystems, food webs and economies. Governments and industry, research institutions and individuals must work together to make headway on this complex challenge that marries mitigation and prevention.
These epic waters are the stuff of legend and lore; a resource that gives life to millions. But as the current flows downstream from the Great Lakes and into the St. Lawrence River, battles continue to be waged beneath the waves. The future remains murky.
This story is from the May/June 2022 Issue
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